This invention relates to portable radio telephone systems. In particular, it relates to portable radio units that are adaptable for connection through a terminal to provide service into the commercial telephone system.
A portable radio telephone is a unit that enables a user to establish wireless connection from essentially any location in a designated service area into the commercial telephone system. The word portable is used in this sense to describe units that can readily be carried on the person as distinct from mobile units which are typically connected to and powered from a vehicle of some sort. Examples of the latter include mobile telephones which extend telephone service to subscribers in vehicles.
Existing mobile telephone systems may provide telephone-like operation. For example, the mobile telephone can initiate and receive calls, it can be identified automatically when it initiates or receives a call, and it can select an available channel automatically from a plurality of channels. However, the presence of a vehicle to serve as a conveyance and the availability of power from the electrical system of the vehicle eases restrictions on the power requirements and size of a mobile telephone. Existing mobile telephones and the systems they operate in are not readily adaptable to portable operation where small size and low power are of the essence. A portable radio-telephone system which provides operation similar to that of existing mobile telephones must of necessity operate differently.
Present-day needs for communication are turning increasingly to the notion that communication should be to and from an individual at his location rather than to a vehicle. The user of a portable radio telephone will also be served best by a unit that operates as much as possible like a telephone so that the user is a telephone caller rather than a radio operator. The portable radio telephone must also be light enough to carry and must be powered adequately for normal use by batteries that can be recharged once a day.
Radio Common Carriers (RCC's) are licensed by the Federal Communications Commission to provide service between radio units and the commercial telephone system. At present RCC's provide portable radio service of several types. The most common is paging where a portable radio which contains only a receiver can receive tone signals or voice messages but cannot talk back. Some systems allow portable transceivers to initiate calls but not receive them. A transceiver is defined here as a combination transmitter and receiver, with or without elements that are common to the transmit and receive paths. Other systems allow portable transceivers to initiate or receive calls but lack essential features of a complete radio telephone system such as automatic channel selection, automatic identification and provisions to prevent users from interfering with each other. The availability of a complete portable radio telephone system will allow RCC's to offer improved service to their subscribers. Other uses by private individuals are also anticipated.
Portable transceivers are widely used for communications in police, industrial, utility and other fleet applications where large groups of users share common concerns. Message traffic on such a communications system is of general interest to all users on the system and it is common practice for all users to monitor broadcasts from a base station or dispatcher and to respond if they are called. Likewise, they must monitor for channel activity before transmitting to prevent interference to communications which may already be in process. In many cases the channel is shared with other fleets or services which often requires monitoring of unrelated message traffic by members in all fleets. These are compromises which commercial users are willing to tolerate. This, however, is not true for the users of radio telephone equipment. By contrast, their message traffic is private and of no concern to other users. Consequently, monitoring is not desirable since it is often viewed as annoying and inconvenient. This necessitates some form of automatically notifying the user of a call intended for him. In a similar fashion, the capability for a user to originate message traffic must also be controlled to prevent inter-user interference. If several channels are to be used it is desirable to have some means of automatic selection of the channel to be used for communication. Automatic channel selection also improves the efficiency of a crowded communications medium. As noted before, many mobile telephone systems provide these features but the capability does not yet exist in a portable radio telephone.
It is an object of the present invention to provide a portable radio-telephone unit.
It is a further object of the present invention to provide a system of communication between commercial telephone systems and users at locations that lack electric power.
It is a further object of the present invention to provide a close approximation to telephone service at a portable transceiver.
It is a further object of the present invention to provide a light and inexpensive portable radio telephone for use in the system of a radio common carrier.
Other objects will become apparent in the course of a detailed description of the invention.